Various systems for the distribution of granular material such as pulverized coal for the feeding of a plurality of furnace burners are known but all offer certain disadvantages in their use. One such known system utilizes a circular housing having a plurality of openings therein. A granular material air mixture is distributed through these openings by centrifugal force. A particular difficulty with this type of system is that the quantity of airborne granular material distributed through each opening cannot be individually regulated. Equal quantities of granular material are fed through all openings.
Another known airborne granular material distribution system includes a knee-shape distributor pipe in an annular housing. An outside ring is turned such that the end of the distributor pipe through which granulate flows is stopped for variable and controllable lengths of time at each of a plurality of apertures in sequence. By controlling the time during which the end of the distributor pipe is aligned with a specific opening, the amount of granulate flowing through each opening is controlled. The major disadvantage of such an arrangement is that individual points of consumption are fed only intermittantly and any change of the tarry time at a particular opening automatically results in variation in the relative feed time of another point of consumption.
In another prior art granulate distribution system, the granulate is distributed to a plurality of points of consumption by means of pulses of controllable length. A disadvantage of this type of system is the intermittent delivery and consequent effects on the operation of the various points of consumption. Certain types of consumers must be fed continuously while the rate of feed is regulated within a predetermined range.
Other airborne granular material distributing systems control the flow rate of the granulate by changing various parameters relating to the airflow at distributor outlets. However, the distribution in such systems is highly dependent upon the condition of the granulate itself. For example, changes in moisture, particle size, and particle friction result in changes in the feed rate thereby making such system somewhat unreliable under certain conditions.